Pearl Nucleus Composition

The Proper Pearl Nucleus

A pearl nucleus is usually made using freshwater mussel shells that has been cut and ground into a polished, spherical bead. Other nuclei do exist, these have been produced from other marine shells, such as from the large black and silver-lipped pearl oysters and from Bironite [SUP]TM[/SUP].

Nacre Deposition will occur over any Solid Object

An oyster's "pearl sac" will secrete nacre over nearly any solid object. This has led to countless attempts to nucleate oysters with material other than shells of course. Even Kokichi Mikimoto attempted the use of silver and gold beads as nuclei for his first experimental cultured pearls, but success has been limited; because of its high success rate and cost, pearly mussel shells are still the preferred choice for pearl farmers as it has been since the early 1900's.

Nucleos Nucleii (5).JPG

Some success has been reported from a new nucleus composed of Bironite [SUP]TM[/SUP], but is not widely used.

Only a Special Material can Create the Best Nucleus

There are several factors that must be in place for the successful culturing of pearls on a large scale. These are the reasons nuclei of non-standard composition has been so quickly rejected in the past:
  • The density of the nucleus must exactly match -or be extremely close- to the density of the pearl. This density is measured to 2.8g/cc.
  • When a pearl is drilled, there is heat produced by this activity. The heat causes the pearl's nacre layer to expand, and the nucleus must expand in the exact same fashion or the pearl will crack. Thus, nacre and the bead must possess the same thermal expansion coefficient. Being the same material, both the bead and its outer nacre layer will survive the drilling procedure, which is necessary for jewelry production.
  • The nuclei must also resist cracking, be free of surface imperfections and remain stable over extended periods of time.
The Best Shell comes from the United States

The material that best fits these criteria are the pearly mussel shells found in the Mississippi River Basin.

Many of the mussels from this area have the added attribute of a thick shell, especially in the joint where the bivalve connects. This thick shell enables harvesters to create large nuclei to be used in culturing larger pearls.

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